The invention relates to a laser system for refractive surgery, having a laser beam source for generating laser beam pulses and having optical means for directing laser beam pulses as a working beam onto or into an eye.
In opthalmology, the term “refractive surgery” with lasers describes the interaction of laser radiation with parts of the eye in order to modify the refractive properties of the eye and therefore its imaging properties, so as to eliminate or at least alleviate imaging defects.
One particularly important example of refractive surgery is the correction of an eye's defective vision by the LASIK technique. In LASIK according to the prior art, the cornea is first cut laterally by means of a microkeratome and the resulting so-called flap is folded to the side. In the cornea's stroma thus exposed, so-called ablation is carried out with laser radiation i.e. tissue is removed according to a so-called ablation profile. The flap is then folded back and a relatively painless and rapid healing process takes place. After this intervention, the cornea has different imaging properties and the defective vision is remedied or reduced.
The above-described lateral incision into the cornea is conventionally carried out in the prior art with a so-called microkeratome, i.e. an oscillating mechanical blade. So-called femtosecond microkeratomes have recently also been used, in which case femtosecond laser pulses are focused into the tissue of the cornea so as to generate so-called laser-induced photodisruptions there in the corneal tissue by closely neighboring focal points of the radiation, which are guided over the corneal tissue so that a cut is finally obtained as in the case of a mechanical microkeratome.
The present invention will be explained in more detail below with reference to the LASIK technique as outlined above. Very generally, however, the laser system according to the invention is also suitable for other refractive surgery methods.
Optical coherence tomography (OCT) has recently gained acceptance as a diagnostic method in opthalmology. OCT has for instance been used for measurements on the retina in vivo, see Lynn M. Savage: “Adaptive optics improves OCT-based retinal imaging” in Biophotonics International, December 2005, 48-49. Owing to axial layer resolution in depth, the measurements carried out by this technique on the retina in vivo deliver images which provide information about disease patterns of the retina before they can actually be seen on the retinal surface, for example using the conventional split lamp technique.
Another application of OCT in refractive surgery is disclosed by U.S. Pat. No. 6,755,319 B1. In this case, photoablation of the cornea is accompanied by an OCT measurement method, in order to measure and therefore monitor the thickness of the cornea during the intervention. Different radiation sources are provided there for the so-called working beam on the one hand, i.e. the laser beam which carries out the refractive surgery, and the measurement beam for the OCT method on the other hand.
Further fundamentals and applications of OCT can be found for example in P. Hsiung, T. H. K O, S. Bourquin, A. Aguirre, P. Herz and J. Fujimoto, “Optical Coherence Tomography”, in Biophotonics International, September 2003, 36-40.